The present invention relates to apparatus for building a stream from particles of smokable material, particularly tobacco shreds. More particularly, the invention relates to improvements in apparatus of the type wherein the stream is formed on an air-permeable conveyor which attracts the particles by suction and moves the particles within a channel having two sidewalls and a bottom wall constituted by the air-permeable conveyor.
It is known to deliver tobacco shreds into the aforementioned channel by way of a duct which receives particles from a mechanical propelling device (such as a rapidly driven carded drum) or in a current of air or another gaseous carrier medium.
Heretofore known stream building apparatus of the above outlined character operates satisfactorily as long as the speed of the conveyor which attracts the particles coming from the duct is below a certain value. However, once such speed is exceeded, the quality of the stream deteriorates and the deterioration progresses as the speed of the conveyor continues to rise. One of the main reasons for deterioration of the quality of the stream of accumulated particles when the speed of the air-permeable conveyor rises above a threshold value, or above a range of threshold values, is that the particles must be fed into the range of the conveyor at a very high speed in order to ensure the formation of a stream containing the required quantity of smokable material per unit length. The particles which are propelled against one side of the rapidly moving air-permeable conveyor (e.g., against the outer side of the upper or lower reach or run of an endless belt conveyor) immediately clog the majority of interstices in the conveyor at the locus or loci of impingement so that the force with which the conveyor attracts the next-following particles is but a small fraction of the initial force (prior to partial clogging). Consequently, the density of the layer which is immediately adjacent to the air-permeable conveyor is much more pronounced than the density of the remaining layer or layers. This results in the making of an unsatisfactory tobacco filler, i.e., the density of such filler is not constant but varies pronouncedly as considered at right angles to its axis. This evidently affects the quality of the ultimate products such as plain or filter tipped cigarettes, cigars or cigarillos.
Another serious drawback of the above described conventional apparatus is that, once the speed of the conveyor (and hence the velocity of particles which are fed to the conveyor) rises above a certain value, the particles are likely to break on impact upon the conveyor so that the apparatus produces a high percentage of so-called short tobacco which also detracts from the quality of the ultimate products and is even more likely to clog the interstices of the air-permeable conveyor. The likelihood of the formation of a high percentage of short tobacco is especially pronounced in that part of the stream building zone where successive increments of the rapidly moving air-permeable conveyor are first contacted by the particles of smokable material, i.e., where the particles impinge directly upon the conveyor rather than upon particles which are already attracted to the conveyor.